ABSTRACT:As the number of processor cores per node increases with multi-core and multi-socket nodes, what are the effects on large-scale scientific application performance? Cielo is the Advanced Simulation and Computing (ASC) program’s newest capability machine. Rated at 1.37 PFLOPS, with dual-socket oct-core nodes linked using Cray’s Gemini interconnect, Cielo represents the latest evolution in multicore-based HPC architectures. We quantify its performance using a suite of applications representing a broad set of requirements of the ASC Tri-lab organizations (Lawrence Livermore, Los Alamos, and Sandia National Laboratories), which are being used for machine acceptance, by comparing with data from its evolutionary ancestors, from dual- to quad- to hex-core. We are finding that improvements to the Cielo node memory architecture reverse the performance degradations. Further, three of the applications are more dependent upon inter-node performance, and thus the change from SeaStar to the Gemini interconnect is being examined.